v19.0.1

A fix release. The brain format (version: 8), bf.yaml, the reply schemas and the search cache are unchanged. Upgrade with uv tool upgrade brain-framework (or update a brain's pin); bf skills DIR refreshes the bf-maintain operations guide, whose only change is naming assistants where it still said prompts.

Fixed

• bf update and bf build --reproject no longer wait for the brain's exclusive writer lock when the search cache is current: they check the cache's pages (PRAGMA quick_check(1), with a 64 MiB page cache) and compare file fingerprints under the shared reader lock, so a refresh with nothing to index runs beside searches and long reads and commits nothing. A refresh that finds changes still takes the writer lock and checks the pages again if another refresh replaced or changed the cache meanwhile.
• The privacy page, the bf-maintain operations guide and the example prompts/.gitignore name an assistant's harness and runs where they still said prompt, as 19.0.0 renamed them.